Method of seasoning sheets containing a solvent



Patented Dec. 5, 1933 UNITED STATES PATENT OFFICE 1 scott, Mass., assignors to The Fiberloid Corporation, Indian Orchard, Mass., a corporation of Massachusetts No Drawing. Application August 26, 1930 Serial No. 477,978

3 Claims. (o1. 1s'-51) Our present invention relates to a method of seasoning sheets of plastic material particularly pyroxylin which contains a residue of the solvent used in manufacturing the sheet. In an application filed August 16, 1930 Serial No. 475,841 by Gustavus J. Esselen, Jr., and entitled Method of seasoning sheets containing a solvent, there is described a method of seasoning pyroxylin or other sheets containing a residue of solvent which persists tenaciously in them and which prior to the invention of the said application was ordinarily removed by drying for a considerable period of time, ordinarily a week or more. By the said Esselen method, the sheet is seasoned by being immersed in a non-solvent liquid capable of displacing the solvent in the sheet or extracting it therefrom then removing the sheet from the bath and then drying out the non-solvent. By this method the process of seasoning pyroxylin sheets can be shortened to a time which on some sizes is considerably less' than a day.

Our present invention is based on the discovery that if the sheet is first momentarily treated with a liquid which we call a tying liquid, this liquid having an afiinity for both the solvent and the non-solvent and having preferably a softening action on the surface of the sheet and is then treated with the non-solvent, the action is accelerated and increased. For instance, if

alcohol is used as the solvent and V. M. P. naphtha as the non-solvent, ethyl acetate may be used for the tying liquid. In that case, the unseasoned sheet of pyroxylin, preferably before it has been allowed to season or harden perceptibly, is treated quickly with ethyl acetate either in the form of a bath'or a vapor. The sheet is then immersed in a bath of non-solvent, i. e. V. M. P. naphtha and the action will be found to be more rapid than is the case if it is immersed in the non-solvent without preliminary treatment with the tying liquid. In practice we also find it desirable to use in both baths a sufficient quantity of the plasticizer employed in the pyroxylin to prevent any considerable extraction of the plasticizer from the pyroxylin sheet during treatment. Also, we find it deisrable to employ a small amount of the tying liquid in the second bath as this also increases the rapidity of action.

As an example of our process, a suitable seasoning bath is made of V. M. P. naphtha and camphor in the proportion of 66 parts of camphor by weight to 100 parts of naphtha together with a small amount of the tying liquid, in this case from 5 to 10 per cent of ethyl acetate. As soon as the sheet is formed and preferably but not necessarily before it has had a chance to season substantially by exposure to the air, it is dipped into and immediately removed from a bath of the tying liquid which in this case is ethyl acetate preferably containing some camphor, for instance, parts of camphor to 100 parts by weight of ethyl acetate and is then immediately dipped into the second or seasoning hath made up in the proportions already described. If the sheet has been allowed to season somewhat before treatment the tying liquid has the effect of overcoming any case hardening which may have occurred and thus facilitates the penetration of the seasoning bath. When treated with the tying liquid as described, the period of immersion in the second or seasoning bath may be shorter than when no treatment with the tying liquid is used. While we have not yet determined what the shortest satisfactory time will be, we have ascertained that on some gauges an immersion of less than an hour in the seasoning bath is sufficient and that the sheet may then be dried in as little as a few hours depending on the degree of seasoning required.

V. M. P. naphtha is commonly known as varnish makers petroleum and is characterized by the fact that it has a flash point not lower than 100 F. While its properties vary with the particular refining company, a typical sample shows a gravity of 47.6, and an initial boiling point of 311 F., and an end point of 411 F.

We have not attempted to determine with any great particularity what liquids can or cannot be used as tying liquids, that is for the first treatment, but we believe that the tying liquid should have an affinity for both the solvent and the non-solvent so that the non-solvent shall be rendered completely miscible with the solvent. We also believe that the liquid, should have the effect of softening the surface of the sheet.

The hereindescribed method embodying my invention produces a sheet having a surface which is at least as good as that of sheets produced by the methods heretofore employed, and also results in the savings already described.

While we have described our invention as we practice it in connection with the manufacture of pyroxylin sheets, we believe it to be applicable to sheets of other substances containing solvents.

We claim: 7

1. The process of seasoning a sheet of pyroxylin or the like containing alcohol, which consists in treating the sheet with ethyl acetate, then treating it with V. M. P. naphtha and then drying the sheet.

2. The process of seasoning a sheet of pyroxyllin or the like containing alcohol, which consists in treating the sheet with ethyl acetate and then treating it with V. M. P. naphtha and drying out the naphtha, both said treating liquids containing a proportion of the plasticizer contained in the sheet.

GUSTAVUS J. ESSELEN, IRVING WEBER. 

